This invention relates generally to multiple-pane windows wherein the panes are separated by a spacer frame and the cavity between the panes is hermetically sealed. More particularly, it concerns a corner key which is inserted in the ends of adjacent spacer frame members and the corner key is locked into engagement with the spacer frame members. In addition, it concerns attaching the spacer frame members to the window frame in several spaced locations around the periphery of the spacer frame. Also, it concerns sealing the cavity between the panes after the spacer frame and additional pane are adhered to the original pane and the window components and cavity are at a temperature substantially equivalent to the ambient temperature, and adding a second seal around the periphery of the spacer frame.
Hermetically-sealed, multiple-pane windows have been available for some time but until recently only as factory made units. Previously, hermetically-sealed units were completed in a factory by preparing a sandwich of pane-spacer frame-pane and sealing the sandwich in an oven large enough to accomodate the entire assembly. The sealant applied to the joints of the sandwich is softened or activated in the oven and the seal is completed while the sandwich is at an elevated temperature.
More recently, methods and components have emerged for making sealed multiple-pane windows on site by adding a spacer frame and an additional pane to an original single pane window and sealing the interfaces between the spacer frame and the panes or the space between the separated panes. The advantage of making sealed windows on site is that the original pane can be utilized; thereby eliminating the cost of one of the panes, removal of the original pane from the window frame and extensive window frame modifications which otherwise would be required to accomodate the additional thickness of the factory made unit. Of course the sealed multiple-pane window provides greater thermal resistance to retard heat transfer through the window. Thus less heat escapes through the window in the winter time and less heat is gained through the window in the summer time, with the overall result of using less energy to heat and cool a building.
The known methods and components for forming sealed multiple-pane windows on site have shortcomings in that the seal on the unit is formed while the window components and cavity air are at an elevated temperature, thereby creating a partial vacuum in the cavity when the unit cools down. The seal may be created at approximately 200.degree. F. and the window subsequently sees an average temperature of 60.degree. F. or low temperatures below zero. The partial vacuum creates inwardly directed forces on the spacer frame, the panes and the sealant. The inwardly directed forces can cause a seal to rupture, thereby allowing ambient air and its attendant moisture or water vapor to enter the cavity, or bow a spacer frame member inwardly at points between corners of the spacer frame, thereby spreading sealant across the interior surface of the panes and creating gaps or separations between the adjacent spacer frame members at the interface between adjacent spacer frame members. The known components and methods for forming sealed multiple-pane windows on site do not provide for locking adjacent spacer frame members together at their interface. Gaps formed between spacer frame members after the seal is formed can provide leaks in the seal and can give the appearance of a lower quality unit